Andy is correct. Acids actually tighten the outer protien structure of the meat limiting penetration of the marinade into the meat. Brines, however, saturate the meat over time, carrying whatever flavorings contained into the meat cells.
Oils are required to release the flavors of some spices and herbs and are another flavor carrier. Though until an imulsifying agent is used, the oil and water tend to remain seperated, with the water as the more dense componant pushing oil to the top surface of the container.
A proper marinating dish only half covers the meat in marinade and requires you to flip the container half way through the marinating process. That allows the oil to sit on top of the meat and penetrate from the top down, carrying the flavors into the meat, while the marinating liquid soaks in from the sides and bottom, again carrying their water soluble flavors in. When the meat is flipped, the same actions occur to the other sides of the meat.
If a brine is used, typically, there is no acidic incredient and so the meat is simply immersed completely.
When I think about it, oil is a penetrating fluid and may very well carry flavors into the meat, in spite of the tightened protien structure from the acid/protien reaction. The acidic citrus, wine, or vinegar would flavor the outer surface while the oil would carry herbs and spice flavors into the meat. But that's just an educated hypothesis based on observation of fluid behavior. Specifically, I'm thinking about how penetrating oil has the ability to enter into places too tight for water to get into through capillary action. The same thing may be true in this application. Again, flipping the meat in a half filled container would be essential to the process.
Seeeeeeya; Goodweed of the North
